When processing semiconductor wafers, particles sometimes contaminate the wafer surface. While every effort is made to clean and filter gases passing through the processing chamber, sometimes chemical byproducts (vapor deposits) of the process itself form particles which temporarily adhere to the chamber inside surfaces. When these particles release from the surface they can fall on the face up surface of a wafer being processed causing contamination, causing the wafer to be rejected. The phenomenon of particle contamination is well known and described in U.S. Pat. No. 4,842,680, issued to Davis, et al., which includes a discussion of the comparison of the particle size with the time to fall one meter in a vacuum environment. Processing wafers in a face down position has been proposed and demonstrated in an effort to avoid such particle contamination and to take advantage of the effects of gravity in eliminating particle and gas distribution contamination.
Texas Instruments, Inc., has at various times proposed face down wafer processing as an improvement in wafer processing technology. However, to avoid contaminating a face down wafer, it is necessary that there be no contact with the down-facing processing surface of the wafer. One technique which has been attempted, is to use pins on the face of or at the edge of the wafer to support the wafer during processing. The use of metal or ceramic pins to support the wafer during processing causes deposition anomalies with inadequate adherence which in turn sometimes leads to flaking of the newly deposited but inadequately bonded material of the coating.
Face down wafer processing techniques are perceived to be especially beneficial when blanket tungsten is being deposited. The face down technique is also perceived to provide greater uniformity in the coating thickness.
The above-mentioned attempts to introduce wafer face down processing techniques have been examined and tested, and ultimately rejected for lack of a reasonably automated way of handling the semiconductor wafer without contaminating the down-facing surface during storage, transfer, and processing. The need exists for a means for supporting a semiconductor wafer in a face down position in a processing chamber which does not mark the processing surface of the wafer and is reasonably suited to automation.